The invention relates to a power screwdriver having a low-noise torque clutch.
In power screwdrivers for driving screws, upon attaining a pre-defined torque the spring force flow from the drive motor to the screw tool is interrupted to avoid excessive driving of the screw. Conventionally, ratchet couplings with two ratchet parts that are spring biased relative to each other are used as torque clutches and each have peripherally inclined beveled cams. The drawback in this type of simple ratchet coupling is the annoying, loud “chattering”, which also results in increased wear of the ratchet coupling.
U.S. Pat. No. 4,655,103 discloses a power screwdriver with a low noise torque clutch, wherein the ratchet coupling is combined with a claw coupling using a common coupling sleeve, wherein a ratchet spring is arranged between the driven ratchet part and the coupling sleeve.
According to U.S. Pat. No. 6,109,149, a power screwdriver has a low-noise torque clutch, which comprises a ratchet coupling and a claw coupling that are combined using a common, axially displaceable, freely rotational coupling sleeve, wherein the ratchet coupling has oppositely oriented peripherally inclined beveled cams and the claw coupling has oppositely oriented, peripheral linear catches. A rigid ratchet spring is arranged between the freely rotational driven ratchet part on the tool shaft and a slack clutch spring is arranged between the driving coupling part connected to the tool shaft and the coupling sleeve. By means of this axial serial arrangement, a high contact pressure of the power screwdriver against the work piece to overcome the rigid ratchet spring is required to engage the ratchet coupling by the axial displacement of the tool shaft and to activate the torque transmission. In addition, this high contact force results in a high quantity of friction heat in the springs rubbing against each other in the override operation.